EASA 2020-0021

Supersedes but retains the requirements of DGAC France AD F-2004-031 R1, which mandates repetitive inspections of the tail rotor hub assembly boot for the presence of hydraulic leak and replacement of certain bearings of the affected hub assembly pitch control rod. Updated AD introduces a modification with improved tail rotor assemblies that incorporate a new bearing with a hydraulic fluid leak-proof feature as terminating action for the repetitive inspections. Prompted by a report of an in-flight yaw control failure, where a tail rotor hub pitch control rod detached from the tail rotor servo-control. The subsequent investigation identified that this event had been caused by the seizure of the tail rotor hub pitch control rod bearing, which suffered from grease dissolving due to contamination by hydraulic fluid leaked from the tail rotor servo-control that came through the assembly boot.